The impending fuel shortage and the increased pressure to reduce pollution resulting from the incomplete combustion of fuel in internal combustion engines, coupled with the tremendous advances in the electronic arts, has provided great impetus to the development of fuel injection systems for internal combustion engines. Such fuel injection systems are highly versatile in sensing engine operating parameters and providing the exact fuel requirements to the engine for particular operating conditions. One such operating condition is the changing of the throttle position which requires an immediate enrichment of the fuel being fed into the engine. Thus, acceleration enrichment circuits have been evolved for electronic fuel injection systems to provide additional fuel in an attempt to immediately meet the fuel requirements of the engine in response to a change in throttle position.
Many acceleration enrichment circuit schemes have been evolved to provide accurate control of fuel delivery over the entire operating range of the engine, including acceleration and deceleration of the engine due to a change in throttle position. Also, certain other requirements of controlling engine operation through fuel control involves generating a signal which is representative of the closed throttle position and the wide open throttle position. Typical prior schemes for the generation of acceleration enrichment pulses are disclosed in U.S. Pat. No. 3,593,692, entitled "Electrical Fuel Injection Arrangement For Internal Combustion Engines" issued to H. Scholl et al., U.S. Pat. No. 3,720,191, entitled "Acceleration Enrichment Circuitry For Electronic Fuel Systems" issued to T. L. Rachel, U.S. Pat. No. 3,726,261, entitled "Acceleration Enrichment Signalling Means For Electronic Fuel Systems," issued to R. G. Sauer, and U.S. Pat. No. 3,926,153, entitled "Closed Throttle Tip-In Circuit," issued to Junuthula N. Reddy.
Referring first to the Scholl patent, fuel enrichment during acceleration is provided by an acceleration enrichment switch attached to the throttle which generates electrical pulses as the throttle is advanced or opened. These pulses are subsequently converted by the fuel control computer into fuel injection pulses which increase the fuel delivery to the engine during acceleration or as a result of opening the throttle. In the Rachel and Sauer patents, a lost motion link is connected between the accelerator pedal and the throttle and a potentiometer generating an electrical signal is mechanically linked to the accelerator pedal. The combination of the accelerator pedal, potentiometer and lost motion link to the throttle provide a means for generating an acceleration demand signal prior to the actual movement of the throttle. Sauer provides two separate circuits for providing fuel enrichment to the engine. The first circuit increases the length of the electrical pulse provided by the electronic computer in proportion to the rate and magnitude of the acceleration demand. The second circuit initiates an immediate electrical pulse to the fuel injectors when the rate and magnitude of acceleration demand exceeds predetermined limits.
The electronic fuel control systems disclosed by Scholl, Rachel and Sauer appear to provide adequate acceleration fuel enrichment when the engine is operating with the throttle at least partially open. However, upon initial commencement of opening movement of the throttle from the closed position there is a momentary lag between the demand for acceleration and the actual response to the engine. For example, in the system disclosed by the Scholl patent, the fuel enrichment pulses are not generated until the throttle is rotated through a predetermined angle to a position where the acceleration switch produces the first pulse. Because of this angular dependency, the time when the first acceleration enrichment pulse is generated is a function of the amount of initial rotation of the throttle.
The Reddy system relates to a throttle tip-in circuit for generating an acceleration fuel enrichment pulse each time the closed throttle signal is terminated when the operator tips in the throttle. The Reddy circuit senses the termination of the closed throttle signal and generates a fuel enrichment pulse independent of the magnitude or rate at which the throttle is open.
As to the Scholl circuit, a certain problem has arisen with respect to the reliability of the circuit. The potentiometer utilized in the Scholl circuit is stepped in nature and does not provide a linear output per degree of angular rotation of the throttle. Further, the resolution of the Scholl system is somewhat limited due to the design of the potentiometer utilized in providing an output signal indicative of the throttle position. It has been found that a continuous signal from a potentiometer is far more desirable to provide a more complete control over the operation of the engine in terms of moving from closed throttle position and in terms of wide open throttle position performance. Further, the Scholl circuit is complex in nature and therefore expensive to manufacture and install.
In a patent to Toshi Suda et al., U.S. Pat. No. 3,786,788, issued Jan. 22, 1974, there is proposed a fuel injection apparatus for an internal combustion engine, the apparatus including a throttle position sensor that produces an analog signal representative of throttle position and thus air velocity to the engine. This throttle position sensor provides a signal to an astable multivibrator circuit, the output frequency of which varies as a function of variations in the throttle position signal. This frequency signal is shaped by means of a pulse shaping circuit, the pulse shaping circuit producing output pulses at the same frequency as the input pulse chain. The output of the shaping circuit is fed to a monostable multivibrator which provides an output pulse train having a fixed on-time and an off-time which varies as a function of the frequency of the pulse train being fed from the shaping circuit. The output of the monostable multivibrator is fed to a current driver circuit which, in turn, is connected to control the solenoid valves associated with the injectors. It will be noted that this Toshi Suda circuit is not an acceleration enrichment circuit which is responsive to the rate of change of throttle position to vary the output pulses to the injectors.